The Detection of Ambiguous Phase in Hard-Limited Signals

In LORAN tracking of radiosondes, the ground tracking station must lock on and track a particular carrier zero crossing in each pulse of a LORAN signal which has been received, hard limited, and retransmitted by a radiosonde target. A variety of causes may result in advance or retard slippage by one (or more) carrier cycle(s). Similar problems of anomalous phase might arise in other phase tracking systems. This paper presents an algorithm for the detection and identification of such anomalous phase events, permitting restoration of proper lock. The basic algorithm and several variations are derived, and their performances are evaluated from the results of a Monte Carlo computer simulation.